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Old 11-27-2007, 05:38 PM
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Hypereutectic Ring Gap??

Hey guys quick question. Engine is a 383 SBC, bore is 4.030, Keith Black hypereutectic pistons. I was told these pistons require a larger ring gap because they expand a lot more. Could anyone who knows please tell me what I should have for the top compression and 2nd compression ring gaps? Right now the top rings only have about 0.015" which I am sure is far too little.

Thanks guys,
Keith

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Old 11-27-2007, 06:16 PM
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Ring gap has nothing to do with the type of piston, but with the material the rings are made of and what the application is, IE: naturally asperated or forced induction.

Hyper PISTONS usually have a very tight fit in the bore, usually .001 smaller than the bore.

To set the RING gap, you need to go by the manufacturers suggestions. Plasma, chrome moly, cast and so on, each will have a slightly different end gap desired measurement. The "rule of thumb" is .004 per inch of bore. But again, you need to use the specs that the ring manufacturer states.

Mark
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Old 11-27-2007, 06:26 PM
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Yea the rings are total seal and the pamphlet that came with them says 0.0045" gap per 1 inch of bore for the top ring for naturally aspirated street applications. It was the guy at the machine shop that said hypereutectic pistons will need a larger gap so that is why I am a little confused on what "larger" should be. I can do some research thanks for your reply.

Keith.
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Old 11-27-2007, 06:28 PM
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KB hyper pistons are of a unique alloy and have high top ring placement.
They want tight piston/cylinder bore clearances and big top ring end gaps.
The pistons do not expand, but they do transfer more heat to the top ring.
Therefore the top ring needs a larger than typical end gap.
Go to the KB/UEM site and follow their recomendations. The more sustained heat load on the piston top , the bigger the ring end gap has to be.

If you set it up as advised your motor will not huff and will make great power for a long long time. If you don;t, your motor will soon huff and puff from scuffed piston rings.
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Old 11-27-2007, 06:29 PM
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http://www.kb-silvolite.com/clearance_pop.php
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Old 11-27-2007, 08:15 PM
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Gap the K-B Hypers too little (as is normal for other types) and you end up with pistons coming apart at the top ring land.

tom
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Old 11-27-2007, 08:59 PM
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Very true. The KB hypers have special gapping requirements. Treat them like other pistons in this respect, and they'll self-destruct in short order. Consult the link above and select your gap needs accordingly. As an example, when I ran them in a NA 350 Chevy for mainly street use, top was .026" and second was .018".
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Old 11-27-2007, 09:48 PM
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Thanks for all the responses guys!! I have one more question since I will need to gap them now. Is there any other method of gapping rings other than the table mounted, hand-operated ring grinder?? I do not have one of these ring grinding machines and it is not so easy for me to get my block to the machine shop for them to do it so if there is any other way of doing it (basic hand file and vice?) I would really appreciate any suggestions that you experienced builders have used in the past.

Thanks guys,
Keith
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Old 11-27-2007, 09:57 PM
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A file works fine. Be sure and file inwards so you don't knock the coating off the outside of the ring. Use a small sharpening stone to smooth the edges where you filed.
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Old 11-28-2007, 04:19 AM
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A new smooth file in a vise. Like above. Try to get the gap as parallel as possible. Deburr with a smooth stone.
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Old 11-28-2007, 10:49 AM
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rings

Mark, the KB Hypereutectic pistons do require a different top ring gap then conventional pistons. This is one time where you need to follow the piston manufacturers proceedures and not the ring manufacturers..

I am not sure what all the engine spec's are but a few things to also look at.

If this engine is on the edge for static compression/cylinder PSI vs the octane of fuel you are going to run you need to pay real close attention to detonation. I have 20 or 25 engines out there with the KB hypereutectic pistons in with only one failure. You can gap the rings correct but if you detonate the engine you WILL break the pistons. This is not a maybe it will happen. The only failure i have ever had with these pistons were due to the customer detonating the engine.

I personally have found that a top ring gap .002" over the recommended is better then on the tight side with no effects on leak down.

Keith
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